Bone conduction hearing aid



`from the remainder of a Patented June l, 1954 2,680,158 BONE CONDUCTION HEARING AID Joachim Wolff, London,

Fortiphone Limited, London, England, a company of Great Britain Application July 10, 1950, Serial N0. 172,789

Claims priority, application Great Britain August 16, 1949 3 Claims.

This invention relates to vbone conduction hearing aids, sometimes termed bone conduction telephones, i. e. to telephones, usually of very small size, which are designed to convey sound to the user by transmitting sound pressure waves through the bones of the users head.

Great diculties are experienced in designing and manufacturing bone conduction telephones to be satisfactory as regards fidelity and response. These diculties arise mainly by reason of the fact that in this type of telephone the air gap in the magnetic system, i. e. the space between the armature and the pole system with which it co-operates, is necessarily very small being usually of the order of about 1/2 to 1 mil. In practice the armature is supported by resilient spring means, for example, a diaphragm, and line adjustment means for adjusting the gap must be provided, for, owing to unavoidable variations in manufacture and materials, it is practically impossible to dispense with adjustment of the air gap.

The gap adjustment means provided in bone conduction telephones as at present known are seldom as simple and convenient to use as is desired. Moreover, the known generally employed gap adjustment means are not such as to avoid undesired tilting of the armature with consequent asymmetry of the air gap. Because ofthe smallness of the air gap the avoiding of such tilting and consequent asymmetry is very impotrant to fidelity and response.

The present invention seeks to provide improved bone conduction telephones in which the air gap adjustment means shall be such that tilting of the-armature can be readily avoided and which shall nevertheless be very simple in construction and convenient and easy to use.

According to this invention a bone conduction telephone unit having a vibratory armature which is resiliently-supported so as to be spaced magnetic system by an air gap is characterised by the provision of three separately adjustable adjusting devices so arranged as to adjust said air gap at three spaced points around it.

Preferably the armature is resiliently supported from theremainder of the magnetic system `and the adjustment devices act at three spaced points on the supporting means. In this casethe supportmeans for the armature is itself carried or supported from the remainder of the magnetlclsystem, at ythree points. In the principal and preferred embodiments of the invention the armature is supported by a England, assignor to spider and each arm being arranged to be adjustably pressed up at its other end against the arcuate means of an adjustment screw which presses against an intermediate In applicants copending application Serial No. 171,921, led July 3, 1950, the claims are directed to the structure of the adjustment devices illustrated.

rlhe invention is illustrated in the accompanying drawings in which Figures 1 to 4 show one embodiment and Figure 5 shows a modification. In the drawings Figure 1 is an elevation partly in section, Figure 2 is a plane with one arm of the three-armed exible support for the armature broken partly in section Referring 'A4 are large and the other three A are small.

The ring magnet sub-assembly consists of one blies are put together.

The sub-assembly C', with which this invention is concerned consists of a top plate CI on which is carried, by means of screws C2 screwing therein, a exible support or diaphragm member for the armature. This support is in the form of a three armed spider C3 the outer ends of the arms of which are drilled to pass the shanks of the screws C2. Each screw C2 passes rst accedas central hole and the armature structure, which is not shown in detail since it forms per se no part of this invention is carried from the centre of the spider by means of its two parts C5, C1 which screw together to Clamp the centre of the spider between them. Deformable adjustment strips C5 which are of springy, deformable metal, lie underneath the arcuate outer parts of the spider arms and each has an upturned end C8 which bears against the underside of the appropriate arcuate outer part about half way between its anchoring screw C2 and the radial part of the arm. Adjustment screws C9 screw into tapped holes in the top plate Ci and each, when screwed up, presses up from underneath against the appropriate adjustment strip C5 about a third of the way along from its anchored end.

The three sub-assemblies are put together in line as shown in Figure 1 with the magnet B between the sub-assemblies A and C. The large holes AG are big enough to pass the heads of the adjustment screws C9 which lie in said holes and are accessible for adjustment. rfhe small holes A5 which are countersunk on the underside pass the shanks of screws Clt which screw into tapped holes in the top plate Cl and hold the sub-assemblies together with the lower face of the armature spaced by a small (adjustable) air gap from the top face of the central pole piece A2 and the top face of the top plate Cl which is co-planar with the said pole piece face.

As will be appreciated with this construction, very fine adjustment may be made to the rest position of each leg of the spider independently and by careful independent adjustment of the three screws accurate parallelism of the vibratory armature with respect to the air gap and the pole system may be obtained and tilting of the armature with consequent assymmetry of the air gap avoided.

A telephone unit as above described and illustrated is mounted in a suitable casing (not shown) -for example of the material known under the registered trade mark of Bakelitesuch mounting being most conveniently fitted by drilling and tapping the centre of the upper or clamping part of the armature structure and employing a bolt which passes through the centre of the back of the casing into this drilled and tapped hole and therefore holds the armature firmly up against the inside of the back of the casing. This holding bolt is thus the sole support for the telephone proper. In use pressure sound waves are transmitted to the back of the casing and then through the casing to the front thereof, which is made of suitably hollow shape as known per se to fit comfortably and efficiently against the sound receiving bone of the wearer.

In the modification shown in Figure 5 each of the deformable strip shaped adjustment members C5 of Figure l is replaced by a coiled spring C55 which may be helical or, as shown, spirohelical. The compression of this spring is adjusted by an adjustment screw C59 and the upper end of the spring i. e. the end remote from the screw C59 has inserted therein the stem part of a taper headed member C58 which performs a function similar to that of the parts C8 of Figure l and bears against the underside of the appropriate arms of the spider C3 where, if desired, a small dimple may be formed to receive the point of the head of the member C58. It is thought that the remainder of Figure 5 will be 4 self-evident from the description already given of Figure 1, like parts in both figures carrying the same references.

Although in the preferred constructions above described the three points at which each adjustment is effectedv are equally spaced around a circle, this is not necessary and they may be irregularly spaced, though the arrangements described are preferred where (as is not always the case) the magnet system is circular. Again, although in the preferred constructions the resilient support means for the armature is likewise carried at three points equally spaced around a circle, this too is not necessary and other arrangements are possible. Thus, for example, instead of using a three legged flexible springy spider as described, a diaphragm-like disc may be used and this disc may be supported at three points around its edge or simply clamped peripherally. Again the invention is not limited to the circular type of construction, for square and rectangular shapes can be used.

i claim:

l. A bone conduction telephone unit comprising a vibratory armature forming part of a magnetic system, resilient support means carried upon the remainder of said system and supporting said armature resiliently therefrom with an air gap therebetween, said support means being formed as a three legged spider with equally spaced arms, and means for adjusting said gap, said last-mentioned means comprising three separately adjustable adjusters each of which acts upon a different arm of said spider.

2. A bone conduction telephone unit comprising a vibratory armature forming part of a magnetic system, resilient support means carried upon the remainder of said system and supporting said armature resiliently therefrom with an air gap therebetween, said support means being formed as a three legged spider with equally spaced arms each comprising a radial portion and an arcuate portion outwardly thereof, and means for adjusting said gap, said last-mentioned means comprising three separately adjustable adjusters each of which acts upon a different arm of said spider at an intermediate point along the arcuate portion thereof.

3. A bone conduction telephone unit compris- ,Ying a vibratory armature forming part of a magnetic system, resilient support means carried upon the remainder of said system and supporting said armature resiliently therefrom with an air gap therebetween, said support means being formed as a three legged spider with equally spaced arms. each comprising a radial portion and an arcuate portion outwardly thereof, and means for adjusting said gap, said last-mentioned means comprising three separately adjustable screw adjusters each of which acts upon a different arm of said spider at an intermediate point along the arcuate portion thereof.

References Cited in the file of this patent 

